The acetal compound is the reaction product of an alditol and benzaldehyde. Alditol acetals, such as MDBS (1,3:2,4-bis (4-methylbenzylidene) sorbitol) and DMDBS (1,3:2,4-bis (4-dimethylbenzylidene) sorbitol) derivative compounds are known compounds which find their utility as an additive in polypropylene. Acetals of substituted and unsubstituted aldehydes are also known to be useful as nucleating agents, gelling agents, processing aids, and strength modifiers in polyolefin resins, polyester resins, deodorant, and antiperspirant compositions; hydrocarbon fuels and paints.
Acetal-alditols are typically prepared by the condensation reaction of an aromatic aldehyde with an alditol containing 6 carbon atoms like sorbitol. For MDBS and DMDBS structures, such reactions involve two moles of the aldehyde and one mole of an alditol.
Several methods for the preparation of acetal-alditols have been reported in U.S. Pat. Nos. 4,267,110, 3,721,682, 4,429,140; 4,562,265; 4,902,807; 5,023,354; 5,731,474 and 6,500,964.
The known processes suffer from several shortcomings. The known processes involve either the use of acidic catalysts or various organic solvents. Though mineral acids serve as good catalysts for the acetalization process, they do not come in contact with all the reactants due to limited solubility of the reactants. Furthermore, the final product resulting from such processes needs to be purified by neutralizing the residual free acid. Though the yields offered by all teachings are acceptable for the practical purposes, all the methods are not effective from the perspective of versatility, environmentally friendliness, energy efficient, reliability, cost-effective, and safe production.
The known processes also employ various organic solvents which necessitates high temperature for carrying out the reaction thereby increasing the cost component. Furthermore, most of solvents are very expensive and they too render the process un-economical. Still furthermore, the use of organic solvents also render these processes non-environment friendly.
Environmental force to minimize waste and re-use materials has prompted studies into “Green” chemistry. Solvents play very important role in chemical reactions; they serve to homogenize and mix reactants, and also act as a heat sink for exothermic processes. One of the biggest industrial concerns is substitute of volatile organic compounds (VOCs) particularly those that are toxic, such as CH2Cl2, and those that are hazardous to handle. Successful attempts to replace or limit the use of VOCs have been made in some cases, and these include processes that use no solvent or new solvent systems such as supercritical H2O, supercritical CO2, fluorous solvents, and recently ionic liquids (ILs).
Phosphonium ionic liquids have been widely employed for various chemical reactions/processes in recent years. Ionic liquids offer distinct advantages in reactions where water formation may hinder or inhibit the rate of reaction, if they are hydrophobic in nature. They are especially used as catalysts or as solvents in chemical reactions like Heck reactions, Suzuki cross-coupling reactions, Henry nitroaldol reaction, esterification, regio-selective hydroamination, hydrogenation, C&O-alkylation, and nitration with excellent conversions, selectivity and stability at high temperatures, and reusability. Similar such applications of the Phosphonium salt ionic liquids have been reported in WO 2006/007703, WO 0041809, U.S. Pat. No. 5,104,840, WO2007023814, JP2009057297, KR20080003855 and US2008221353.
None of the hitherto reported processes for preparation of MDBS and DMDBS have employed ionic liquids as catalysts and/or reaction medium. There exists a need for process for preparation of MDBS and DMDBS which uses ionic liquids as the catalyst and/or reaction medium. There also remains a need for a process for preparation of acetals, particularly MDBS and DMDBS which does not employ any expensive solvents or mineral acids.